puch maxi runs better at half throttle

Matthew Libhart /

Everyone,

First post to the Army. '78 Puch Maxi Luxe seems to run as good or better at about 3/4 throttle as it does at full throttle, especially when climbing hills. I'm wondering if that's normal or if something may be a little off (carb?).

Thanks.

Re: puch maxi runs better at half throttle

See Ya Moped Army /

Sounds like it's 4-strokingg. There's too much fuel and not enough air. You need to either decrease the size of the main jet or increase airflow.

Re: puch maxi runs better at half throttle

Matthew Libhart /

Thanks. Air filter is probably the original from 1978. I'll try that first.

Re: puch maxi runs better at half throttle

Jason Luther /

my maxi had the same problem, for it has too much air. i guess there is asupposed to be a tube with a plug in it coming off of the air box and into the frame, mine doesnt have that, so i taped over about 2/5 of the hole. eventually i will buy i bigger jet.-jason

Re: puch maxi runs better at half throttle

Ben Van Zoest /

Now I am getting confused, one says there is too much air the other says to little air. Which one is't that causes four stroking?

Re: puch maxi runs better at half throttle

Jason Luther /

four stroking is too much gas (among other things). try covering up a little of your air hole and see if that helps. its easy, its free, its reversable. or get a new plug and try a plug chop.-jason

Re: puch maxi runs better at half throttle

Matthew Libhart /

I've seen that tube on pictures of an airbox, and mine is also missing this tube. I'll try the tape, that's easy enough.

When you say too much gas causes 4-stroking, it sounds like you don't mean it's rich. It just means that there's too much airflow (like what would happen if you rode w/o the air filter? Is that correct?

Thanks everyone.

Re: puch maxi runs better at half throttle

Matthew Libhart /

All,

Just pulled the spark plug. Guess that should be the first thing that's done. It was moist and nearly black. I got a flashlight and turned the magneto and watched the piston head inside the cylinder. I then checked the points. They're opening just as piston starts the downstroke. This seems way off, shouldn't the points be opening just as the piston reaches (or just a little before) TDC?

Not sure if this timing issue would cause a black plug, but it could cause some serious knock I think.

Thanks again.

Re: puch maxi runs better at half throttle

Usually the points should open at 2mm before TDC, I believe. In the case of Puchs, they do not like either too little air nor too much air. Play around with the airbox intake hole with some tape and see what happens if you cut some air off.

Re: puch maxi runs better at half throttle

Isn't a wet, black plug usually an indication of running too rich?

Re: puch maxi runs better at half throttle

Matthew Libhart /

That's what I thought too (wet & black plug = rich).

I'm not sure how to adjust the carb for this. I haven't put a new air filter on it yet, but if I pull the air filter off, it still has the knock. And maybe I'm hearing something other than the piston. The knock seems to be louder if the back tire is on the ground and stationary (at idle speed) and less loud, but still very noticeable, when the ped is up on the stand and the wheel is allowed to turn when the engine is at idle speed. Does this sound like a clutch issue?

I advanced the timing as far as I could, it's a little better now but still seems a little late and the knock is still present. Not sure it's possible to do anything about it if the stater plates are adjusted all the way in the counterclock wise direction.

I'm going to ride it in a bit and I'll see how it does at full throttle, which is what got the discussion going in the first place.

Thanks again everyone.

Re: puch maxi runs better at half throttle

Ben Van Zoest /

Detonation definitely MUST occur before TDC as late as possible. Get an 1/2" wide engineers ruler one scale is metric wedge something firmly in the cooling fins for edge reference insert ruler through spark plug hole manually turn magneto until ruler extents out to max TDC note mm reading go around once more. Points should open +/- 2.4mm less than first reading. In case your points won't open at least .010 (worn fiber striker) you still can rotate back mount plate to get the critical timing right.

Re: puch maxi - half throttle partly solved

Matthew Libhart /

Took the carb apart yesterday. The jet needle was on the bottom most notch - richest setting. Moved it to the second notch from the top. Plug looks 100% better. Still have a bit of a knock and seems a bit sluggish on the low end, but that may be helped by some new ATF fluid. Thanks again everyone.

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